Power Management System for a Microbial Fuel Cell and Microbial Electrolysis Cell Coupled System

ABSTRACT

Various embodiments of the invention include a power management unit (PMU) to simultaneously control the production of hydrogen and electricity for external use in an MFC-MEC coupled system. In one embodiment, the PMU includes low voltage electronic switches using MOSFETs, and a PWM controller. The PWM controller creates timing waveform necessary to operate the switches. In other embodiments, the switches can be replaced by any switching regulator capable of operating at low operating voltage and currents that yield high efficiency. Such a system can be used in a waste-water treatment facility.

CROSS REFERENCE TO RELATED APPLICATIONS

This application is a conversion to a non-provisional application under 37 C.F.R. §1.53(c)(3) of U.S. provisional application No. 61/612,981, entitled “Power Management System for a Microbial Fuel Cell and Microbial Electrolysis Cell Coupled System”, filed on Mar. 20, 2012.

BACKGROUND OF THE INVENTION

Power Management Unit (PMU), in general is used to control power applied to an electrical load depending on load conditions and/or input power applied to the system. PMUs are implemented using solid-state device such as BJTs or FETs and capacitors and/or inductors. PMUs are switching regulators capable of boosting or bucking a DC input voltage applied to them.

Microbial Fuel Cells (MFC) are used to generate electricity while treating waste-water. Microbial Electrolysis cells (MEC) are used to produce hydrogen gas from waste-water by applying external power to it.

PMUs have been used to control the output power based on the power generating capabilities of the microbial fuel cell. MFC and MEC coupled systems are low-voltage systems (around 1V) and low current in the order of few hundred mA. Hence, the PMUs require electronic switches and other associated circuitry capable of operating under such low voltages and producing very little voltage drop across them.

Carbon Nanotubes and nanowires are used to improve charge transfer between anaerobic bacteria and anode surface of a microbial fuel cell.

Inverters together with PMUs and/or DC combiners are used to apply power to the electrical grid or local factory such as waste-water treatment plant either from an array of solar panels, stack of solid-oxide fuel cells using natural gas or other fuels, and farm of wind turbines.

BRIEF SUMMARY OF THE INVENTION

In this invention, PMU has been designed that controls the power applied to an electrical load consisting of a hydrogen producing fuel cell and an electrical system that supplies power to the consumer such as waste-water treatment plant simultaneously.

The PMU allows a means to control the production of hydrogen or electricity depending on demand conditions.

Traditionally, hydrogen production in a microbial electrolysis cell (MEC) or similar is controlled by varying the applied voltage through a potentiometer in a laboratory setting or through a solid-state power supply in a commercial setting. The “excess” voltage that was not utilized in hydrogen production has not been used to power other electrical loads such as electrical grid, commercial and residential facilities and waste-water treatment plants.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 illustrates a typical electrical circuit connection between MFC-MEC systems to control hydrogen production.

FIG. 2 illustrates an electrical circuit connection of MFC-MEC coupled system using electronic switches and controller to control hydrogen production and supply power to an external load simultaneously.

FIG. 3 is an electrical circuit diagram using a switched capacitor implementation of Power Management Unit.

FIG. 4 is a timing diagram of the PMU using PWM controller and electronic switches.

FIG. 5 details the working of switched capacitor based PMU over time.

FIG. 6 is a schematic diagram setup for an electrical circuit simulation in TINA™.

FIG. 7 is the equation that governs the voltage applied to the MEC.

FIG. 8 is the equation that governs the output voltage of PMU that is available to power an electrical system.

FIG. 9 is a timing diagram that corresponds to more power being made available to an external electrical system while less power made available for hydrogen production in MEC.

FIG. 10 is a timing diagram that corresponds to more power made available for increased hydrogen production while less power made available to the electrical system.

FIG. 11 is a block diagram of the MFC-MEC fuel cell system with built-in PMU shown as a basic building block.

FIG. 12 shows an array of the MFC-MEC fuel cell system configuration to use in a typical waste-water treatment plant.

DETAILED DESCRIPTION OF THE INVENTION

As shown in FIG. 1, the equivalent circuit of MFC is represented by 10, and that of MEC by 11. The potentiometer 12 is used to control the voltage and hence power applied to the MEC in a typical laboratory setting to control the hydrogen production. The drawback of this scheme is that the power is dissipated as heat in 12 reducing the efficiency of the system.

FIG. 2 shows the block diagram of the PMU design using electronic switch circuits 13 and 14 to obtain high efficiencies. The switch circuits 13 and 14 are controlled by 15, a PWM controller with a feedback from output in order to maintain the set output voltage. The switch circuits can be implemented using a switching regulator. This switching regulator can be of either capacitor or inductor based switching circuits.

FIG. 3 shows a typical implementation of PMU using switched-capacitor based circuit topology. This is a desired topology due to low currents and voltages of the MFC-MEC coupled system. Switches S₁-S₅ can be a MOSFETs (or ultra-low voltage semiconducting switching device) with low channel resistance to minimize power loss. PWM controller can be implemented using an off-the-shelf IC.

FIG. 4 shows the timing diagram of the PWM controller. By adjusting the width of the timing pulse to S₁ with respect to the overall timing period T, the desired voltage is supplied to the cathode chamber of MFC. The width of the timing pulses, T₂ and T₃ determine the output voltage of the regulator for external use. T₁, T₂ and T₃ are all required to be non-overlapping timing pulses.

FIG. 5 details the working of the switched capacitor voltage regulator over a complete cycle of operation. The typical frequency of operation of the PWM controller is of the order of 100 KHz.

FIG. 6 is a schematic diagram of the switched-capacitor based voltage regulator in a circuit simulator called TINA™. VG₁-VG₃ represent the PWM controller operating at about 100 KHz repetition rate. S₁-S₅ represent ideal switches with some resistance to reflect the channel resistance of MOSFETs. It is also set to have a low switching threshold voltage (˜0.5V). The MFC and MEC is represented by a battery element with a reasonable internal resistance (5 ohms) typical of a large volume cell. Capacitors C₁ and C₂ are a typical low leakage capacitors such as tantalum. R_(load) mimics the typical load expected of a single MFC-MEC coupled system.

FIG. 7 and FIG. 8 are the equations governing the voltage applied to the MEC and external load respectively based on timing periods, external load resistance, switch resistance and capacitor values.

FIG. 9 shows the timing waveform of the simulation setup corresponding to minimum hydrogen production or more power to external load. The voltage delivered to the external load is about 1.3 volts. The amount of voltage applied to cathode chamber of MEC is about 0.2 volts.

FIG. 10 shows the timing waveform of the simulation setup corresponding to the maximum hydrogen production or less power to the external load. The voltage delivered to the external load is about 0.2 volts. The amount of voltage applied to cathode chamber is about 1.0 volt.

FIG. 11 shows the basic building block of the MFC-MEC coupled system with a built-in PMU. The physical size of the building block is predominantly determined by the energy densities required at a waste-water treatment facility.

FIG. 12 shows the inter-connection of the basic building block to form a larger electrical system. The building blocks are connected in series to increase the terminal voltage of the combined system while in parallel to increase the current production. Several of the systems are connected in parallel once a give terminal voltage has been setup in a DC combiner box before feeding into an Inverter. The inverter is then connected to either an electrical grid or used locally to power the plant or residential or commercial facility. 

1. What I claim as my invention is the design of a power management unit that allows simultaneous production of hydrogen and electricity for external use in a MFC-MEC coupled system.
 2. I claim the electrical circuit configuration wherein electronic switch is used to control power applied to the MEC while another electronic switch is used to vary the power made available for external use.
 3. I claim the design of a high-efficiency PMU (>90%) using electronic switches consisting of any form of semi-conducting material including and not limited to organic semi-conductors for system described in claim
 1. 4. The PMU is either a switched-capacitor or inductor-less or inductor based voltage regulator circuit using any form of PWM controller to control the operation and timing of electronic switches for system in claim
 1. 5. A MEC-MFC coupled system with built-in PMU can serve as a building block in an electrical system which has a series and/or parallel combination of such building blocks to form a power plant.
 6. One or more inverters can be used to connect the system described in claim 1 in order to produce AC power to connect either to an electrical grid or to power a local commercial and residential facilities or to power a waste-water treatment plant. 